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The compound hazard of gas and coal spontaneous combustion in underground coal mines is a major factor limiting the safe production of coal mines, and the oxidation characteristics of coal spontaneous combustion of residual coal in the mining area are closely related to the residual gas and the starting temperature. We reviewed the research progress of solid-gas adsorption theoretical models, systematically analyzed the research methods, experimental platforms and recent progresses involved in the competitive adsorption characteristics of multi-gas, microscopic pore structure evolution and microscopic group evolution characteristics of gas-bearing coal at different temperatures by domestic and foreign scholars, and discussed the characteristics of pore characteristics changes and the evolution laws of macromolecules and functional groups of coal under different temperature conditions.

The research on coal breaking mechanism by high-pressure water jet can provide theoretical basis for water jet equipment manufacturing and construction technology research. In this paper, based on the investigation of a large number of related literatures at home and abroad, we summarized the relevant theories of coal breaking mechanism by high pressure water jet. From the perspective of the structure of water jet and mechanical properties of coal, this paper introduces the stress wave theory of crushing, quasi-static elastic fracture theory, the theory of cavitation and broken and crack propagation mechanism of broken coal at all stages about crushing theory researches. In view of the applicability and limitations of various current coal breaking theories, it is suggested that further research can be carried out from three directions: improving the coal breaking mechanism of water jet, two-phase jet and new jet mode.

Objective To explore the clinical significance of monitoring neuron specific enolase (NSE), carbohydrate antigen 125 (CA125), and carbohydrate antigen 199 (CA199) in patients with pneumoconiosis. Methods A retrospective analysis was conducted among 222 patients with pneumoconiosis admitted to this hospital from January 2018 to December 2022. The patients were divided into three groups according to the stage of pneumoconiosis (stage I, II, and III). The serum levels and abnormal rates of NSE, CA125, and CA199 among these groups were compared. Results Among the 222 patients with pneumoconiosis, 51 (22.97%) were in stage I, 52 (23.42%) were in stage II, and 119 (53.61%) were in stage III. There were statistically significant differences in serum NSE and CA125 levels among pneumoconiosis patients at different stages (P < 0.001), and serum NSE and CA125 levels in patients at stage III were higher than those in stage I and stage II (P < 0.001). There was no statistically significant difference in serum CA199 level among pneumoconiosis patients at different stages (P = 0.163). The abnormal rates of serum NSE, CA125, and CA199 levels among 222 patients were 45.05%, 27.93%, and 2.70%, respectively. There were statistically significant differences in serum NSE and CA125 abnormal rates among pneumoconiosis patients at different stages (both P < 0.001), and both showed an increasing trend with the increase of stage. Conclusions Monitoring serum NSE and CA125 in patients with pneumoconiosis can indicate the progression of their condition and provide references for the treatment plan. [ABSTRACT FROM AUTHOR]

The breakdown voltage (Vb) was studied for (Bi0.5Na0.5)TiO3 (BNT)-added positive temperature coefficient of resistance (PTCR) ceramic samples based on (Ba0.659Pb0.341)TiO3, which were prepared by a traditional solid-reaction method and sintered in an air atmosphere. By measuring the electrical properties and microstructures of the materials, the breakdown voltage was found to depend on neither the room-temperature resistivity nor the maximum resistivity, but on the grain size (D) of the samples to some extent. With a decrease in the grain size, the Vb value increases rapidly, especially for samples with fine grains. With the help of Heywang-Jonker theory, the depletion width (LD) was calculated to determine the dominant factor affecting the Vb value using the approximate equation Vb= 600 × LD/D + 100; i.e., the breakdown voltage is approximate directly proportional to the ratio of LD/D. However, the room-temperature resistivity increased slightly with LD/D, and the PTC performance remained at a high level (α > 34%, Rmax/Rmin > 1 × 103). It is more advantageous to increase the breakdown voltage by adjusting LD/D than by reducing grain size alone. The variations in the grain size and the depletion layer width of different samples are mainly due to the generation of VNa′ and VBiʺ′ inside of the lattice. The ratio of LD/D can also be used to explain the variation in room-temperature resistivity. [ABSTRACT FROM AUTHOR]

The pore distribution characteristics of coal not only directly affect the gas storage and migration ability in coal seam, but also directly affect the development process of physical adsorption and chemical reaction between coal and oxygen. Therefore, in-depth study of the pore distribution characteristics of coal is conducive to the reasonable classification and evaluation of coal reservoirs, and then study and analyze the laws of gas storage and migration in coal seams and the low-temperature oxidation reaction mechanism of coal, improve the accuracy of gas content prediction and gas extraction efficiency, and describe the process of coal spontaneous combustion in detail. We have systematically summarized the current research theories and methods of pore distribution characteristics of coal through a large number of relevant literature investigations, and compared and analyzed various research theories and methods, pointed out their respective advantages and disadvantages. Finally, it is proposed that the next step can be carried out from three directions: accurate measurement of micro-pores and reasonable characterization at full scale, research on microscopic effects of coal pores, and establishment of accurate coal medium models.

Combined with the occurrence characteristics of China’s low permeability coal seam and the advantages and disadvantages of various permeability enhancement technologies, the technical methods to improve the permeability of coal seam are classified and compared, and the technology, equipment, application effect, existing problems and defects and applicable conditions of each permeability enhancement method are systematically sorted out. The development trend of permeability enhancement technology is prospected, and it is pointed out that permeability enhancement technology will work in combination with various permeability enhancement methods, and permeability enhancement equipment will develop towards intelligent and unmanned direction.

Based on the systematic investigation, this paper summarizes the four important development stages of the prediction technology of mine gas emission in China from 1950s to now. It focuses on the basic principles, application scope, advantages and disadvantages of the source based prediction method, mine statistical method, gas geological mathematical model method, grey prediction method, neural network prediction method and combination prediction method. The main problems of each prediction method are analyzed in detail with the field application status. Finally, centering on the development goals of mine mechanization and intelligentization, three technological breakthroughs are proposed: improving the scientific selection of predictive parameters of source separation, promoting the modularization and integration of gas geological model prediction technology, and establishing information-based high-end fusion model, which points out the direction for future research on gas emission prediction technology.

The gas occurrence mechanism of deep coal seam is an important theoretical basis to guide the safe and efficient mining of deep coal and gas resources. Compared with the shallow coal seam, the occurrence environment of the deep coal seam has the characteristics of high stress, high temperature, high gas pressure and low permeability, which determines the unique characteristics of the deep gas occurrence and the technical problems faced by the deep resource output. We systematically reviewed the influence of stress, temperature, pressure and permeability on the gas occurrence laws of deep coal seam, pointed out the shortcomings of single physical field influence research, and made clear that the multi-field coupling environment is the objective condition for the study of gas mechanism of deep coal seam, and pointed out the direction for the study of gas occurrence mechanism of deep coal seam.

Based on the water jet slotting coal seam permeability increase technology, the stress distribution state of the coal after slotting is analyzed, and the radial and tangential stresses of the slotted borehole are calculated. Based on the theoretical analysis of the influence radius of the water jet slotting, the technical process based on the water jet slotting drilling arrangement is determined. According to the field measured data, the statistical dynamic indicators were analyzed to verify the effect of coal seam gas extraction after water jet slotting. The research shows that compared with the conventional drilling, the gas extraction concentration with water jet slotting drilling is increased by 3.6 times, the flow is increased by 2.7 times, the pure flow is increased by 9.7 times, the average wind discharge of the west wing of the upper third mining is decreased by 0.68 m3/min and reduced by 26.98%. The gas content of the water jet slotting drilling section is more reduced by 0.48 m3/t; when the extraction radius is 3.0 m, the extraction time of the water jet slotting drilling section is 41days. The comparison was shortened by 43 days.

Abstract: ZnO thin films were prepared on glass or on homo-buffer/glass by a RF magnetron sputtering method at RF power of 100–550W. The structural and Raman characteristics of the films were analyzed by X-ray diffraction and Raman scattering. There appeared a sharp peak of 1080.2cm−1 near the A1(2LO) mode (1156cm−1) of ZnO in the Raman spectra when the RF power was higher than 300W. In this case, the (100) peak of ZnO film appeared obviously. It was speculated that the Raman mode at 1080.2cm−1 was induced by the ordered distribution of Zn i defects in ZnO lattice. [Copyright &y& Elsevier]